The present invention relates to a brush holder structure in an electric motor for use as a component of electric equipment or the like and a mold structure for manufacturing brush holders.
Generally, in some electric motors of this type, brush holders for housing brushes held in slidable contact with a commutator provided on a rotor shaft and an end bracket for rotatably supporting the rotor shaft are both integrally molded with a gear frame for housing and supporting a worm gear mechanism. The worm gear mechanism comprises a worm formed around the distal end portion of the rotor shaft and a worm wheel held in mesh with the worm. When such a gear frame is molded, a mold for forming the brush holders is required to have a pair of first molds set in butt relationship along the axis of the rotor shaft for forming at least the outer surfaces of the proximal end side walls of the brush holders with respect to the rotor shaft and the end faces of the brush holders on the side where the brushes are projecting from the brush holders, and a pair of second molds set in butt relationship from the outer peripheral side toward the axis of the rotor shaft for forming the inner surfaces of four surrounding walls of each brush holder.
In the conventional mold, however, since the second molds are set in butt relationship from the outer peripheral side toward the axis of the rotor shaft, the brush holder is made hollow throughout from the inner peripheral end, through which the associated brush projects, to the outer peripheral end thereof. As a result, resilient means for resiliently pressing the brush is arranged in the form of torsion resilient means attached to a resilient means attachment which is provided on the outside of the brush holder, and a free end of the resilient means is pressed against the rear surface (the end face on the outer peripheral side) of the brush for resiliently holding the brush in slidable contact against a commutator. Meanwhile, there is a strong demand for reduction in weight and size of electric motors as well. To meet this demand, the end bracket also needs to be designed more compactly. This makes it difficult to ensure a space in the end bracket for the resilient means attachment on the outside of the brush holder. Therefore, the brush holder is required to be designed so that the resilient means for pressing the brush is fitted in the brush holder.